1. Technical Field
The present invention relates to a method of optical proximity correction (OPC). More particularly, the present invention relates to a precise method of OPC and a computer-readable medium recording the same.
2. Description of the Related Art
In semiconductor manufacturing processes, in order to transfer an integrated circuit layout onto a semiconductor wafer, the integrated circuit layout is first designed and formed as a photo-mask pattern. The photo-mask pattern is then proportionally transferred to a photoresist layer positioned on the semiconductor wafer.
As the design pattern of integrated circuit becomes smaller and due to the resolution limit of the optical exposure tool, optical proximity effect will easily occur during the photolithographic process for transferring the photo-mask pattern with higher density. The optical proximity effect will cause defects when transferring the photo-mask pattern, such as right-angled corner rounding, line end shortening, and line width increasing/decreasing. In order to avoid the above-mentioned defects caused by the optical proximity effect, the semiconductor process uses a computer system to perform an optical proximity correction (OPC) method of the integrated circuit layout. The corrected integrated circuit layout is then designed as a photo-mask pattern and is formed on the photo-mask.
To check the effects of OPC, photo-mask patterns with OPC have to be verified based on the prediction of photoresist patterns defined thereby, which is conventionally based on a simulation of the exposure intensity distribution at the photoresist layer. By finding out the local extreme intensity, predicted photoresist patterns are obtained from the distribution. According to the photoresist patterns predicted, further OPC is done to further modify the photo-mask patterns so that the later predicted photoresist patterns are closer to those required by the IC process.
Since the design patterns of integrated circuit may be symmetric or asymmetric, it is not proper to assume that the local extreme intensities of different photo-masks lay on the center of gap or of width of the patterns of photo-mask. If assumption of the local extreme intensity is wrong, it could not produce a precise OPC and the yield of integrated circuit may be decreased.